Since the launch of Sputnik 1 in 1957, many manmade objects have been launched into space. While some of those objects have traveled far beyond Earth (e.g., Voyager 1 and 2) and some of those objects have returned to Earth (e.g., Apollo 11), a large number of objects or portions of objects remain in orbit around the Earth. These objects are referred to as orbital debris. For example, orbital debris may include the non-limiting examples of derelict spacecraft, upper stages of launch vehicles, carriers for multiple payloads, debris intentionally released during spacecraft separation from its launch vehicle or during mission operations, debris created as a result of spacecraft or upper stage explosions or collisions, solid rocket motor effluents, and tiny flecks of paint released by thermal stress or small particle impacts. More than 21,000 orbital debris larger than 10 cm are known to exist. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles smaller than 1 cm is estimated to exceed 100 million.
In order to evaluate the risk to spacecraft (e.g., satellites, the space station, manned and unmanned missions, etc.) currently in use or planned for use, it is important to be able to identify and classify orbital debris. An important tool for identifying and/or classifying orbital debris is the use of the bi-directional reflectance distribution function (BRDF). The BRDF for a known object may be measured in ground based lab setting. A known object's BRDF may then be compared to the BRDF measured for an unknown space debris in order to identify and/or classify the unknown item. Current methods for measuring BRDFs in ground based settings rely upon robotic manipulators or handheld cameras, which is time consuming and introduces the possibility of systemic and/or random errors into the measurement. Therefore, a need exists for improved methods and corresponding devices for measuring the BRDF of a known object.
The present invention provides improved methods and associated devices for measuring the BRDF of an object.